Salt of a pyrimido[6,1-A]isoquinolin-4-one compound

ABSTRACT

The present invention relates to a pharmaceutically acceptable acid addition salt of: (i) 9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one (RPL554); and (ii) ethane-1,2-disulfonic acid, ethanesulfonic acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, phosphoric acid or sulfuric acid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage application of PCT/GB2016/050313, filed 10 Feb. 2016, which claims priority to Great Britain Application No. 1502260.1, filed 11 Feb. 2015, the disclosures of which are hereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to salts of a pyrimido[6,1-A]isoquinolin-4-one compound and pharmaceutical compositions comprising these salts. Medical uses of such salts are also described.

BACKGROUND OF THE INVENTION

A number of factors must be considered when developing an appropriate form of an active pharmaceutical ingredient (API) for formulation for administration to human subjects. These include efficacy, toxicity, stability, solubility/dissolution and acidity/basicity. Different formulations comprising a number of different forms of the API are usually evaluated. The outcomes of such evaluations are unpredictable.

Solubility/dissolution, stability and acidity/basicity can be very important factors to control for an API. Solubility/dissolution must be at an appropriate level to enable delivery of a sufficient dose of the active ingredient to have the desired therapeutic effect in a patient. The solubilities of different salt forms of a therapeutic agent are unpredictable.

The stability of an API must be sufficient to ensure that the product is shelf stable for long periods. Acidity/basicity is of importance for orally administered drugs and inhaled drugs as overly acidic formulations may cause discomfort to subjects upon administration.

RPL554 (9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one) is a dual PDE3/PDE4 inhibitor and is described in WO 00/58308. As a combined PDE3/PDE4 inhibitor, RPL554 has both anti-inflammatory and bronchodilatory activity and is useful in the treatment of respiratory disorders such as asthma and chronic obstructive pulmonary disease (COPD). The structure of RPL554 is shown below.

Owing to its applicability in the treatment of respiratory disorders, it is often preferable to administer RPL554 by inhalation. Franciosi et al. disclose a solution of RPL554 in a citrate-phosphate buffer at pH 3.2 (The Lancet: Respiratory Medicine November 2013; 1(9):714-27. DOI: 10.1016/S2213-2600(13)70187-5). The preparation of salts of RPL554 has not been described.

SUMMARY OF THE INVENTION

It is a finding of the present invention that certain salts of RPL554 have highly desirable properties. In particular, specific pharmaceutically acceptable salts of RPL554 have been found to have improved water solubility and improved solubility in appropriately pH buffered solutions. The increased solubility in buffered solutions allows for higher drug loading in solutions of more mild pH, which could lead to greater tolerance of patients to inhalation or oral administration. Certain specific salts of RPL554 have also been found to be crystalline. Crystalline salts are typically more stable than amorphous forms, and are particularly desirable if the RPL554 is to be successfully delivered as a dry powder or in other formulations in which the active ingredient is present in the solid state.

Furthermore, certain salts of RPL554 have been found to have desirable intrinsic dissolution rates which can lead to improved bioavailability. Particular salts of RPL554 have also been found to be well suited to pressurised metered dose and dry powder formulations.

The thermal stabilities of certain salts of RPL554 have also been found to be better than the thermal stabilities of other salts. Such salts are desirable as they are resistant to variation in temperatures without changes in form. Stability to changes in humidity is also desirable.

Accordingly, the present invention provides a pharmaceutically acceptable acid addition salt of:

-   -   (i)         9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one         (RPL554); and     -   (ii) ethane-1,2-disulfonic acid, ethanesulfonic acid,         methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic         acid, hydrochloric acid, hydrobromic acid, phosphoric acid or         sulfuric acid.

The invention further provides a pharmaceutical composition comprising a pharmaceutically acceptable acid addition salt of the invention and a pharmaceutically acceptable excipient, carrier or diluent.

The invention further provides a pharmaceutically acceptable acid addition salt of the invention for use in the treatment of the human or animal body.

The invention further provides a pharmaceutically acceptable acid addition salt of the invention for use in the treatment or prevention of a disease or condition selected from asthma, allergic asthma, hay fever, allergic rhinitis, bronchitis, emphysema, bronchiectasis, chronic obstructive pulmonary disease (COPD), adult respiratory distress syndrome (ARDS), steroid resistant asthma, severe asthma, paediatric asthma, cystic fibrosis, lung fibrosis, pulmonary fibrosis, interstitial lung disease, skin disorders, atopic dermatitis, psoriasis, ocular inflammation, cerebral ischaemia, inflammatory diseases and auto-immune diseases.

The invention further provides a method of treating or preventing a disease or condition selected from asthma, allergic asthma, hay fever, allergic rhinitis, bronchitis, emphysema, bronchiectasis, chronic obstructive pulmonary disease (COPD), adult respiratory distress syndrome (ARDS), steroid resistant asthma, severe asthma, paediatric asthma, cystic fibrosis, lung fibrosis, pulmonary fibrosis, interstitial lung disease, skin disorders, atopic dermatitis, psoriasis, ocular inflammation, cerebral ischaemia, inflammatory diseases and auto-immune diseases in a subject, which method comprises administering to said subject an effective amount of a pharmaceutically acceptable acid addition salt of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows XRPD patterns of solids isolated from RPL554 salt formation wherein the acid used is: sulfuric (A), phosphoric (B), hydrochloric-aqueous (C), ethanesulfonic (D), hydrobromic (E), methanesulfonic (F) and naphthalene-1,5-disulfonic (G). The XRPD pattern of the RPL554 free base is also shown (H).

FIG. 2 shows XRPD patterns of solids isolated from RPL554 salt formation wherein the acid used is: ethane-1,2-disulfonic (A), p-toluenesulfonic (B), benzenesulfonic (C), hydrochloric-anhydrous (D), 2-naphthalenesulfonic-1 equivalent (E) and 2-naphthalenesulfonic-4 equivalents (F). The XRPD pattern of the RPL554 free base is also shown (G).

FIG. 3 shows XRPD patterns of solids isolated from RPL554 salt formation wherein the acid used is: 1-hydroxy-2-naphthoic-1 equivalent (A), 1-hydroxy-2-naphthoic-4 equivalents (B), pyromellitic-1 equivalent (C) and pyromellitic-4 equivalents (D). The XRPD pattern of the RPL554 free base is also shown (H).

FIG. 4 shows the gravimetric vapour sorption (GVS) profile of RPL554 hydrochloride.

FIG. 5 shows XRPD patterns of RPL554 hydrochloride for 0% humidity (A), 90% humidity (B) and as initially input (C).

FIG. 6 shows the GVS profile of bis-RPL554 ethane-1,2-disulfonate.

FIG. 7 shows XRPD patterns of bis-RPL554 ethane-1,2-disulfonate for 0% humidity (A), 90% humidity (B) and as initially input (C).

FIG. 8 shows the intrinsic dissolution of the sulfate (A), methanesulfonate (B) and ethanesulfonate (C) salts of RPL554.

FIG. 9 shows the intrinsic dissolution of free base (F), ethane-1,2-disulfonate (E), hydrobromide (D), hydrochloride (C), benzenesulfonate (B) and p-toluenesulfonate (A) salts of RPL554.

FIG. 10 shows the intrinsic dissolution of the sulfate salt of RPL554 over 24 hours.

FIG. 11 shows the aerodynamic assessment of selected RPL554 base and salt pMDI formulations (mean values, n=3, ±SD), where the bars from left to right are: free base 134/227 10% EtOH; ethanesulfonate 227; methanesulfonate 134a; benzenesulfonate 134a; sulfate 134a; and ethanedisulfonate 227 10% EtOH.

FIG. 12 shows the aerodynamic assessment of RPL554 free base and salt variant DPI formulations, where the bars from left to right are: free base; ethanesulfonate; p-toluenesulfonate; methanesulfonate; benzenesulfonate; sulfate; hydrochloride; ethane-1,2-disulfonate; and hydrobromide.

DETAILED DESCRIPTION OF THE INVENTION

The RPL554 salts of the invention are pharmaceutically acceptable acid addition salts of RPL554 and ethane-1,2-disulfonic acid, ethanesulfonic acid, methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, hydrochloric acid, hydrobromic acid, phosphoric acid or sulfuric acid, or solvates thereof.

Typically, the acid is ethane-1,2-disulfonic acid, ethanesulfonic acid, methanesulfonic acid, benzenesulfonic acid, hydrochloric acid, or sulfuric acid.

An acid addition salt of RPL554 is a salt formed by reaction of RPL554 with an acid. RPL554 is weakly basic compound and may be protonated to form a cationic species which forms a salt with the conjugate base of the acid used.

The acid addition salt of RPL554 may be selected from RPL554 ethane-1,2-disulfonate, RPL554 ethanesulfonate, RPL554 methanesulfonate, RPL554 benzenesulfonate, RPL554 p-toluenesulfonate, RPL554 hydrochloride, RPL554 hydrobromide, RPL554 phosphate, RPL554 sulfate and solvates thereof. Typically, the salt is selected from RPL554 ethane-1,2-disulfonate, RPL554 phosphate, RPL554 methanesulfonate, RPL554 hydrochloride, RPL554 sulfate, and solvates thereof.

Solvates of salts are solid salts which comprise molecules of solvent. The solvent may be any solvent but is often water or an alcohol such as ethanol. The solvate may therefore be a hydrate or an alcoholate such as an ethanolate. The RPL554 salts may be anhydrates, monohydrates, dihydrates or higher hydrates, or non-stoichiometric hydrates.

The stoichiometry of the salts may be one to one, or it may be two to one, or one to two, or indeed any other ratio of acid to base.

The salt of the invention may for instance be RPL554 ethane-1,2-disulfonate or a solvate thereof. The stoichiometry of the RPL554 ethane-1,2-disulfonate salt is typically about 2:1 API:counter ion. The salt of the invention may for instance be RPL554 phosphate or a solvate thereof. The stoichiometry of the RPL554 phosphate salt is typically about 1:1 API:counter ion. The salt of the invention may for instance be RPL554 methanesulfonate or a solvate thereof. The stoichiometry of the RPL554 methanesulfonate salt is typically about 1:1 API:counter ion. The salt of the invention may for instance be RPL554 hydrochloride or a solvate thereof. The stoichiometry of the RPL554 hydrochloride salt is typically about 1:1 API:counter ion. The salt of the invention may for instance be RPL554 sulfate or a solvate thereof. The stoichiometry of the RPL554 sulfate salt is typically about 1:1 API:counter ion.

The stoichiometry of the salts can be determined by techniques known to those skilled in the art, such as ¹H NMR.

The salts of the invention may be produced by any suitable method for producing salts of active pharmaceutical molecules. Typically, the salts are produced by dissolving RPL554 in a solvent, for instance dichloromethane or dimethylformamide, and subsequently adding a solution of the desired acid, for instance a solution of the acid in ethanol or THF. The salt may then be isolated by filtration, or by removing the solvent from the resulting composition, for instance by drying under vacuum. The salt concentrate may be subsequently triturated with an antisolvent, for example methyl tert-butyl ether and collected by filtration, or it may be purified and isolated by other means.

The RPL554 salt of the invention typically has a purity of greater than or equal to about 90%, greater than or equal to about 95% or greater than or equal to about 97%. The percentage may be calculated as area % based on HPLC separation. Thus, the invention provides a solid composition comprising greater than or equal to about 90%, greater than or equal to about 95%, or greater than or equal to about 97%, of a salt of RPL554 as defined herein.

The pharmaceutical composition according to the invention comprises a pharmaceutically acceptable acid addition salt as defined herein and a pharmaceutically acceptable excipient, carrier or diluent. The pharmaceutically acceptable excipient, carrier or diluent may be any suitable pharmaceutically acceptable excipient, carrier or diluent. These are well known to the skilled person.

The diluent may be any pharmaceutically acceptable diluent. The diluent is typically suitable for administration by inhalation. Examples of suitable diluents include water, ethanol and glycerol. The diluent is preferably water. The diluent is preferably sterile. The diluent may alternatively be selected from solid diluents such as lactose, dextrose, saccharose, cellulose, corn starch and potato starch. The diluent may contain buffer components to control the pH. The buffers may be derived from phosphate, citrate or acetate. The diluent may also contain sodium chloride.

The pharmaceutical composition may comprise for instance: lubricants, e.g. silica, talc, stearic acid, magnesium or calcium stearate, and/or polyethylene glycols; binding agents; e.g. starches, arabic gums, gelatin, methylcellulose, carboxymethylcellulose or polyvinyl pyrrolidone; disaggregating agents, e.g. starch, alginic acid, alginates or sodium starch glycolate; effervescing mixtures; dyestuffs; sweeteners; wetting agents, such as lecithin, polysorbates, laurylsulphates; and, in general, non toxic and pharmacologically inactive substances used in pharmaceutical formulations. Such pharmaceutical preparations may be manufactured in known manner, for example, by means of mixing, granulating, tableting, sugar coating, or film coating processes.

Compositions which are liquid dispersions for oral administration may be syrups, emulsions and suspensions. The syrups may contain as carriers, for example, saccharose or saccharose with glycerine and/or mannitol and/or sorbitol.

Compositions which are suspensions or emulsions may contain as carrier, for example a natural gum, agar, sodium alginate, pectin, methylcellulose, carboxymethylcellulose, or polyvinyl alcohol. The suspension or solutions for intramuscular injections may contain, together with the active compound, a pharmaceutically acceptable carrier, e.g. sterile water, olive oil, ethyl oleate, glycols, e.g. propylene glycol, and if desired, a suitable amount of lidocaine hydrochloride.

Solutions for injection or infusion, or for inhalation, may contain as carrier, for example, sterile water or preferably they may be in the form of sterile, aqueous, isotonic saline solutions.

Preferably, the composition of the invention is formulated for administration by inhalation.

The pharmaceutical composition may be a dry powder. Typically, a pharmaceutical composition which is a dry powder is delivered using a dry powder inhaler.

Typically, the dry powder inhaler is a Clickhaler, Novolizer, Certihaler, Diskus, Multihaler, Gyrohaler (Vectura Group plc), Aerolizer, Handihaler or Tubospin (PH&T S.p.A.), Acu-Breathe unit (Respirics, Inc.), Conix (Cambridge Consultants Limited), Miat Monohaler (Cyclohaler), Eclipse (Sanofi-Aventis), e-flex (Microdrug AG), Flowcaps (Hovione), Prohaler (Valois Pharm), DirectHaler (Trimel BioPharma), Single Dose SDD (Manta technologies), Monodose (Miat SpA), TwinCaps (Hovione), GenX (CCL), SkyeHaler (SkyePharma), EasyHaler (Orion Pharma), or Taifun (Akela Pharma Inc.), with Clickhaler, Novolizer, Diskus and Aerolizer being the preferred dry powder inhalers.

Typically, a pharmaceutical composition which is a dry powder is prepared by milling, spray drying, fluidized spray drying, spray congealing, micronization, controlled crystallization, co-crystallization, ultrasound assisted crystallization, freeze drying or particle precipitation of the salt. Typically, the resulting powder has a particle size with a mass median aerodynamic diameter from about 1 μm to about 10 μm, preferably from about 3.5 μm to about 10 μm, more preferably from about 4 μm to about 5.5 μm, or from about 5 μm to about 10 μm, or from about 5.5 μm to about 10 μm or from about 6 μm to about 10 μm. The resulting powder may instead have a particle size with a mass median aerodynamic diameter from about 2 μm to about 5 μm, for instance from 2.5 μm to about 4.5 μm.

A dry powder pharmaceutical composition may comprise (a) from 50.0 to 99.8 wt % lactose powder and (b) from 0.2 to 50.0 wt % of a salt of RPL554 according to the invention. A preferred dry powder pharmaceutical composition comprises (a) from 80.0 to 99.8 wt % lactose powder and (b) from 0.2 to 20.0 wt % of a salt of RPL554 according to the invention. For instance, the powder pharmaceutical composition may comprise (a) from 95.0 to 99.8 wt % lactose powder and (b) from 0.2 to 5.0 wt % of a salt of RPL554 according to the invention. In some cases, the content of the salt may be approximately 1.0 wt %. For example, the powder pharmaceutical composition may comprise (a) from 99.2 to 99.8 wt % lactose powder and (b) from 0.2 to 0.8 wt % of a salt of RPL554 according to the invention.

In some cases, the pharmaceutical composition suitable for inhalation is in the form of a composition for a pressurised metered dose inhaler (pMDI). The pharmaceutical composition for administration by pMDI may comprise (a) a salt of RPL554 as defined herein and (b) one or more propellants. The one or more propellants are typically selected from hydrofluoroalkanes such as HFA 134a and HFA 227a. The formulation may further comprise (c) ethanol. The formulation may further comprise (d) a surfactant, for instance Tween 80. For example, the pharmaceutical composition may comprise (a) from 0.1 to 1.0 wt % of a salt of RPL554 as defined herein, (b) from 80.0 to 99.9 wt % of a hydrofluoroalkane, (c) from 0.0 to 19.0 wt % ethanol and (d) from 0.0 to 0.5 wt % Tween 80. In one embodiment, the pharmaceutical composition comprises (a) from 0.1 to 0.9 wt % of a salt of RPL554 as defined herein and (b) from total of HFA 134a and/or HFA 227a. Alternatively, the pharmaceutical composition may comprise (a) from 0.1 to 0.9 wt % of a salt of RPL554 as defined herein, (b) from 88.0 to 90.0 wt % total of HFA 134a and/or HFA 227a, (d) from 0.05 to 0.15 wt % of Tween 80 and (c) ethanol to balance.

In some cases, the pharmaceutical composition is an aqueous solution. Thus, the pharmaceutical composition is typically obtainable by dissolving a pharmaceutically acceptable salt of the invention in an aqueous solution. Dissolving the salt may comprise adding a solid form of the salt to the aqueous solution and agitating the resulting mixture to dissolve at least part of the salt. The resulting mixture may be heated to improve dissolution. pH may also be adjusted appropriately.

The concentration of the salt of the invention in the composition which is an aqueous solution is typically greater than or equal to about 0.1 mg/ml, greater than or equal to about 1 mg/ml or greater than or equal to about 2.5 mg/ml. For instance, the concentration of the salt of the invention in the aqueous solution is typically from about 1 mg/ml to about 50 mg/ml, for instance from about 2 mg/ml to 25 mg/ml or from about 2.5 mg/ml to 10 mg/ml.

Typically, the pharmaceutical composition which is an aqueous solution further comprises one or more buffers. The buffers are pharmaceutically acceptable buffers. Thus, the aqueous solution may be a buffered aqueous solution. The pharmaceutical composition may for instance be obtainable by dissolving the salt in a buffered aqueous solution. The buffers may be any buffers suitable for use in pharmaceutical composition, for instance a pharmaceutical invention suitable for inhalation. The one or more buffers are typically selected from acetate, citrate or phosphate buffers. The buffered aqueous solution typically comprises a phosphate buffer and/or a citrate buffer (for instance a citro-phosphate buffer). Citrate buffers include citric acid, sodium citrate and mixtures thereof. Phosphate buffers include phosphoric acid, monosodium phosphate, dibasic sodium phosphate and mixtures thereof. Acetate buffers include acetic acid and salts of acetic acid.

The pH of the buffered aqueous solution in the absence of RPL554 salt is typically from about 3.0 to about 7.0, for instance from about 4.0 to about 5.0. Formation of a pharmaceutical composition by dissolving a salt in the buffered aqueous solution may cause the pH of the buffered solution to vary. For instance, the pH may decrease on dissolution of the salt. This variation is typically small, however.

The pH of the pharmaceutical composition obtainable by dissolving the salt in an aqueous solution (e.g. a buffered aqueous solution) is typically greater than or equal to about 2.0. For instance, the pH of the pharmaceutical composition may be greater than or equal to about 3.0 or greater than or equal to about 4.0. The pH of the composition may be from about 3.0 to about 6.0, or from about 3.5 to about 5.5.

The aqueous solution may be a saline solution or a buffered saline solution. The aqueous solution may comprise from about 0.1 to about 2.0 w/w % saline (i.e. NaCl).

The pharmaceutical formulation may be a liquid pharmaceutical composition suitable for administration by inhalation comprising a diluent and a suspension of particles of a salt of RPL554 as described herein. The suspended particles of the salt of RPL554 typically have a particle size distribution with a Dv50 (median particle size by volume) value of from about 0.2 μm to about 5 μm. The Dv50 may be as measured using laser diffraction. The diluent may be water or a hydrofluoroalkane. The liquid pharmaceutical composition may further comprise a buffer, a solvent such as ethanol or a surfactant such as Tween (e.g. Tween 20 or 80).

The invention also provides a nebulizer comprising a pharmaceutical composition according to the invention which is an aqueous solution. The nebulizer is typically loaded with the pharmaceutical composition. The nebulizer typically comprises from about 1 mL to about 200 mL, more typically from 1 mL to 20 mL of the liquid pharmaceutical composition.

Nebulizers use compressed air to aerosolise a liquid pharmaceutical composition into an aerosol that is inhaled into a subject's respiratory tract. Examples of nebulizers include a soft mist nebulizer, a vibrating mesh nebulizer, a jet nebulizer and an ultrasonic wave nebulizer. Suitable nebulizer devices include the Philips I-Neb™ (Philips), the Pan LC Sprint (Pari GmbH), the AERx® Pulmonary Delivery System (Aradigm Corp.) and the Pari LC Plus Reusable Nebulizer (Pari GmbH).

The nebulizer is typically able to aerosolize the RPL554 salt solution into an aerosol comprising particles with an MMAD of from about 1 to about 10 μm, preferably from about 3 μm to about 10 μm, more preferably from about 4 μm to about 5.5 μm, or from about 5 μm to about 10 μm, or from about 5.5 μm to about 10 μm or from about 6 μm to about 10 μm. The MMAD may be from about 2 μm to about 5 μm, for instance from 2.5 μm to about 4.5 μm.

The invention also provides a pharmaceutically acceptable acid addition salt as defined herein for use in the treatment of the human or animal body. The invention also provides a pharmaceutical combination as defined herein for use in the treatment of the human or animal body.

Treatment of the human or animal body typically comprises the treatment or prevention of a disease or condition selected from asthma, allergic asthma, hay fever, allergic rhinitis, bronchitis, emphysema, bronchiectasis, chronic obstructive pulmonary disease (COPD), adult respiratory distress syndrome (ARDS), steroid resistant asthma, severe asthma, paediatric asthma, cystic fibrosis, lung fibrosis, pulmonary fibrosis, interstitial lung disease, skin disorders, atopic dermatitis, psoriasis, ocular inflammation, cerebral ischaemia, inflammatory diseases and auto-immune diseases.

Often, the disease or condition is asthma or chronic obstructive pulmonary disease (COPD).

The invention also provides a method of treating or preventing a disease or condition as defined herein in a subject, which method comprises administering to said subject an effective amount of a pharmaceutically acceptable acid addition salt of the invention.

An effective amount of RPL554 is typically from about 0.001 mg/kg to 50 mg/kg for a single dose. An effective amount of RPL554 is often from about 0.001 mg/kg to 1 mg/kg for a single dose. For instance, an effective amount may be a dose of from about 0.01 mg to about 500 mg, or from about 0.01 mg to 100 mg, preferably from about 0.1 mg to about 6 mg. A single dose of RPL554 may be from 0.05 mg to 5 mg or from 0.5 mg to 3 mg, for instance about 1.5 mg. Doses may be administered daily. For instance, the dose of RPL554 may be from 0.001 mg/kg/day to 50 mg/kg/day, typically from 0.001 mg/kg/day to 10 mg/kg/day or from 0.01 mg/kg/day to 1 mg/kg/day. These doses are typically the nominal dose charged to the inhaler. The liquid pharmaceutical composition may be administered once, twice or three times a day, or may be administered twice, three times, four times or five times a week. The composition may be administered as often as required by the patient.

The invention also provides the use of a pharmaceutically acceptable acid addition salt as defined herein in the manufacture of a medicament for the treatment of a disease or condition as defined herein.

The following Examples illustrate the invention.

EXAMPLES

Initial Investigations

Instruments and Methods

Automated counter ion screening—Counter ion screening of the API was performed using a Crissy platform supplied by Zinsser Analytic using Zinsser control software version 7.0.9. The Crissy platform was used to dispense stock solutions of API, counter ions and solvents followed by mixture agitation by vortex shaking. A 48 position block format for sample tubes was utilised for the screen which was conducted at ambient temperature. Sample tubes containing solids of interest were isolated by filtration and dried in vacuo at ambient temperature.

HPLC Conditions—RPL554 Chemical Purity by HPLC

Diluent Preparation—deionised water: acetonitrile (1:1). Both were mixed thoroughly and allowed to reach room temperature before use.

Blank Solution—the blank solution consists of diluent.

Sample Solution Preparation—Approximately 7 mg of sample was accurately weighed into a 14 ml glass vial and dissolved in approximately 14 ml of diluent, mix thoroughly and use these solutions for injection.

Column: X-Bridge Phenyl 150×4.6 mm, 3.5 μm particle size (Ex-Waters, part number 186003355); Mobile Phase: A—Purified Water: Trifluoroacetic Acid (100:0.1); B—Acetonitrile: Trifluoroacetic Acid (100:0.1); Flow Rate: 1.0 ml·min⁻¹; Injection Volume: 10 μl; Detection: UV @ 254 nm; Column Temperature: 30° C.; Post Run: 5 min

Time (min) % A % B Gradient: 0 95 5 2 95 5 15 5 95 20 5 95 22 95 5

Expected retention time for RPL554: 11.3 minutes

Solution proton NMR—¹H NMR spectra were collected using a JEOL EX 270 MHz spectrometer equipped with an auto-sampler. The samples were dissolved in a suitable deuterated solvent for analysis. The data was acquired using Delta NMR Processing and Control Software version 4.3.

X-Ray Powder Diffraction (XRPD)—X-Ray Powder Diffraction patterns were collected on a PANalytical diffractometer using Cu Kα radiation (45 kV, 40 mA), 0-0 goniometer, focusing mirror, divergence slit (½″), soller slits at both incident and divergent beam (4 mm) and a PIXcel detector. The software used for data collection was X′Pert Data Collector, version 2.2f and the data was presented using X′Pert Data Viewer, version 1.2d. XRPD patterns were acquired under ambient conditions via a transmission foil sample stage (polyimide—Kapton, 12.7 μm thickness film) under ambient conditions using a PANalytical X′Pert PRO. The data collection range was 2.994-35° 20 with a continuous scan speed of 0.202004° s⁻¹.

Differential Scanning calorimetry (DSC)—DSC data were collected on a PerkinElmer Pyris 4000 DSC equipped with a 45 position sample holder. The instrument was verified for energy and temperature calibration using certified indium. A predefined amount of the sample, 0.5-3.0 mg, was placed in a pin holed aluminium pan and heated at 20° C. min⁻¹ from 30 to 350° C., or varied as experimentation dictated. A purge of dry nitrogen at 60 ml·min⁻¹ was maintained over the sample. The instrument control, data acquisition and analysis were performed with Pyris Software v9.0.1.0203.

Thermo-Gravimetric Analysis (TGA)—TGA data were collected on a PerkinElmer Pyris 1 TGA equipped with a 20 position auto-sampler. The instrument was calibrated using a certified weight and certified Alumel and Perkalloy for temperature. A predefined amount of the sample, 1-5 mg, was loaded onto a pre-tared aluminium crucible and was heated at 20° C. min⁻¹ from ambient temperature to 400° C. A nitrogen purge at 20 ml·min⁻¹ was maintained over the sample. The instrument control, data acquisition and analysis were performed with Pyris Software v9.0.1.0203.

Water content by Karl Fischer titration—Approximately 0.2 g of sample was accurately weighed by difference and transferred into the Karl Fischer vessel. The sample was then mixed for 600 seconds to ensure that it was fully dissolved and then titrated against Hydranal Composite 5. Analysis was performed in duplicate.

Gravimetric Vapour Sorption—Sorption isotherms were obtained using a Hiden Isochema moisture sorption analyser (model IGAsorp), controlled by IGAsorp Systems Software V6.50.48. The sample was maintained at a constant temperature (25° C.) by the instrument controls. The humidity was controlled by mixing streams of dry and wet nitrogen, with a total flow of 250 ml·min⁻¹. The instrument was verified for relative humidity content by measuring three calibrated Rotronic salt solutions (10-50-88%). The weight change of the sample was monitored as a function of humidity by a microbalance (accuracy+/−0.005 mg). A defined amount of sample was placed in a tared mesh stainless steel basket under ambient conditions. A full experimental cycle typically consisted of three scans (sorption, desorption and sorption) at a constant temperature (25° C.) and 10% RH intervals over a 0-90% range (60 minutes for each humidity level). This type of experiment should demonstrate the ability of samples studied to absorb moisture (or not) over a set of well-determined humidity ranges.

Example 1—Preparation and Evaluation of Salts of RPL554

Solutions containing either 1 or 4 equivalents of the counter ion as set out in Table 1 were charged to agitated 23.4 ml solutions of RPL554 in dichloromethane (DCM) at a concentration of 17.1 mg/ml and at a temperature of 40° C. and allowed to cool to ambient temperature. The composition of the counter ion solutions are shown in Table 2.

TABLE 1 Acid counter ions Equivalents Hydrochloric, aqueous 4 Sulfuric 1 Phosphoric 1 Hydrobromic 4 Naphthalene-1,5-disulfonic 4 Ethane-1,2-disulfonic 1 Ethane sulfonic 1 p-Toluene sulfonic 4 Methane sulfonic 4 Benzene sulfonic 4 2-Naphthalene sulfonic 1 and 4 Hydrochloric, anhydrous 4 1-Hydroxy-2-naphthoic 1 and 4 Pyromellitic 1 and 4

TABLE 2 Volume Volume used, used, Conc., μL for 1 μL for 4 Acids Solvent M equivalent equivalents Hydrochloric acid Ethanol 2 12.5 50 Sulfuric acid Ethanol 2 12.5 50 Phosphoric acid Ethanol 2 12.5 50 Hydrobromic acid Ethanol 2 12.5 50 Naphthalene-1,5-disulfonic THF 1 25 100 acid Ethane-1,2-disulfonic acid Ethanol 2 12.5 50 Ethane sulfonic acid THF 2 12.5 50 p-Toluene sulfonic acid Ethanol 2 12.5 50 Methane sulfonic acid THF 2 12.5 50 Benzene sulfonic acid Ethanol 2 12.5 50 2-Naphthalene sulfonic acid THF 1 25 100

Solids were observed to form with phosphoric, naphthalene-1,5-disulfonic and ethane-1,2-disulfonic acids. The volume of the reaction solvent was reduced by nitrogen stream to ca 2-5 ml. Tert-butylmetyl ether (TBME), 8 ml, was then charged to the mixtures affording precipitates and gummy solids which were agitated overnight. This afforded suspensions in some cases as well as returning gummy solids and mixtures which were further manipulated with DCM and TBME via trituration to afford suspensions. The mixtures were agitated for a further 4 hours prior to the isolation of the solids by filtration which were then dried in vacuo at 45° C.

The chemical purities of the isolated solids were determined by HPLC and are detailed in Table 3. The solids isolated with sulfuric, ethane sulfonic, methane sulfonic, 1-hydroxy-2-naphthoic, pyromellitic and hydrochloric (anhydrous) acids had slightly reduced chemical purities. There was no significant degradation of RPL554 with the counter ions and procedures employed.

TABLE 3 ¹H NMR Shift in ¹H NMR API Solid Chemical Filtrate resonances to counter ion Acid counter ions Equivs. colour purity, area % colour of RPL554 Stoichiometry Sulfuric 1 Off white 95.15 Colourless Yes, salt N/A Phosphoric 1 Very pale 98.43 Yellow No N/A yellow Hydrochloric, 4 White 98.56 Tan Yes, salt N/A aqueous Ethane sulfonic 1 White 97.94 Tan Yes, salt 1:1 Hydrobromic 4 White 98.15 Orange Yes, salt N/A Methane sulfonic 4 White 97.92 Colourless Yes, salt 1:2 Naphthalene-1,5- 4 White 99.08 Amber Yes, salt 1:1 disulfonic Ethane-1,2- 1 White 98.09 Tan Yes, salt 1:1 (approx) disulfonic p-Toluene sulfonic 4 White 98.37 Colourless Yes, salt 1:2 Benzene sulfonic 4 Pale 98.06 Colourless Yes, salt 1:2 yellow Hydrochloric, 4 Very pale 96.62 Colourless Yes, salt N/A anhydrous yellow 2-Naphthalene 1 White 98.99 Pale yellow Yes, salt 1:1 sulfonic 2-Naphthalene 4 Off white 98.31 Colourless Yes, salt 1:2 sulfonic 1-Hydroxy-2- 1 Yellow No 1:0.5 naphthoic 1-Hydroxy-2- 4 Yellow Slight shift 1:1.35 naphthoic Pyromellitic 1 Pale 96.32 Slight shift 1:0.92 yellow Pyromellitic 4 Pale 95.81 Slight shift 1:1.47 yellow

¹H NMR spectra of the solids revealed shifts in the resonances of RPL554 consistent with salt formation except for phosphoric, 1-hydroxy-2-naphthoic and pyromellitic acids. The stoichiometry of the salts derived from sulfonic acid counter ions was found to be either 1:1 or 1:2, RPL554 to counter ion. For 1-hydroxy-2-naphthoic and pyromellitic acids the stoichiometries varied and salt formation was not definitive.

The XRPD patterns (FIG. 1, FIG. 2 and FIG. 3) of the isolated solids revealed that modified versions of RPL554 had been generated with the appropriate acid counter ion equivalents and were of varying crystallinity and did not resemble RPL554 free base except for the solid isolated from 1-hydroxy-2-naphthoic acid, 1 equivalent. The XRPD pattern of the solid isolated from 1-hydroxy-2-naphthoic acid, 1 equivalent, contained reflections common to RPL554 together with additional reflections and indicated that this solid might perhaps be a solid mixture of RPL554 and 1-hydroxy-2-naphthoic acid. The XRPD patterns obtained are detailed in Table 4. Crystalline XRPD patterns were observed for most salts.

TABLE 4 Stoichiometry, RPL554 to counter Acid counter ion ion Form Sulfuric not determined Crystalline Phosphoric not determined Crystalline Hydrochloric, aqueous not determined Crystalline Ethane sulfonic 1:1 Crystalline Hydrobromic not determined Crystalline Methane sulfonic 1:2 Crystalline Naphthalene-1,5-disulfonic 1:1 Weakly crystalline Ethane-1,2-disulfonic 1:1 (approx) Crystalline p-Toluene sulfonic 1:2 Crystalline Benzene sulfonic 1:2 Crystalline Hydrochloric, anhydrous not determined Very weakly crystalline 2-Naphthalene sulfonic, 1 1:1 Crystalline equivalent 2-Naphthalene sulfonic, 4 1:2 Crystalline equivalents 1-Hydroxy-2-naphthoic, 1 1:0.5 Crystalline - possible equivalent mixture 1-Hydroxy-2-naphthoic, 4 1:1.35 Crystalline equivalents Pyromellitic, 1 equivalent 1:0.92 Very weakly crystalline Pyromellitic, 4 equivalents 1:1.47 Crystalline

The physico-chemical characteristics of the salt candidates were determined. These are given in Table 5.

TABLE 5 CP of Stoichiometry, pH of RPL554 by API: Solubility as aqueous Form of solid HPLC, Counter ion by Form of solid TGA, weight RPL554 in suspension/ post water Counter ion area % NMR or IC XRPD/NMR DSC, ° C. reduction, % water, mg/ml solution maturation Sulfuric - ethanol 98.82 ND Crystalline Endo broad, 2.37% up to ca 2.52 3.28 No change solution Ethanol solvate, Salt formation 130 - Form 85° C. - loss of Suspension stoichiometric change? water Endo, 193.5, melt Sulfuric - ethanol ND ND¹ Crystalline ND NR ND ND ND solution Ethanol solvate, Salt formation Repeat stoichiometric Sulfuric - ND 1:≈1 (0.84) Crystalline Endo broad, 0.53% up to ca 12.17 1.87 No change aqueous solution Salt formation 122 - Form 55° C. - loss of Suspension change? water Endo, 185 - 3.45% coincident Form change/ with endo at melt? 185° C. - de- Endo, 264 - hydration melt? Phosphoric 99.35 ND Crystalline Endo, 148.9, 2.83% coincident >22.52 3.08 Not known No Salt formation melt with endo Solution solid recovered assumed Phosphoric ND 1:≈1 (0.77) Crystalline Endo, 145.8, NR ND ND ND Repeat Salt formation melt assumed Hydrochloric 98.48 ND Crystalline Endo, 156.6, 4.17% to ca 4.95 3.84 No change aqueous source Salt formation melt 125° C. - loss of Suspension water Hydrochloric ND 1:≈1 (0.90) Crystalline Endo, 156.8, NR ND ND ND aqueous source Salt formation melt Repeat Ethane sulfonic 98.79 1:1 Crystalline Endo broad, 1.54% up to ca >21.69 3.04 Not known No Salt formation 108.9 - Form 50° C. - loss of Solution solid recovered change? water Endo, 219.2, melt Ethane sulfonic ND 1:1 Crystalline Endo broad, NR ND ND ND Repeat Salt formation 86.4 - Form change? Endo, 219.6, melt HBr 97.90 ND Crystalline Endo, 174.1, 3.74% to ca 3.66 3.20 No change Salt formation melt 135° C. - loss of Suspension water Methane sulfonic 97.37 1:1 Crystalline Endo, 219.7, 0.5% up to ca 21.15 2.69 Not known No Salt formation melt 65° C. - loss of Solution solid recovered water Naphthalene-1,5- 99.29 1:0.5 Crystalline Endo, 266.2, 2.12% up to ca 0.00 3.37 No change disulfonic Salt formation melt 110° C. - loss of Suspension water Ethane-1,2- 98.91 1:0.5 Crystalline Endo, 216.8, 1.95% up to ca 1.89 3.72 No change disulfonic Salt formation melt 120° C. - loss of Suspension water p-Toluene 96.86 1:1 Crystalline Endo, 207.5, 1.28% up to ca 0.70 3.40 No change sulfonic Salt formation melt 85° C. - loss of Suspension water Benzene sulfonic 97.61 1:1 Crystalline Endo, 161.6, 2.43% up to ca 1.47 3.43 No change Salt formation melt 140° C. - loss of Suspension water Hydrochloric 96.98 ND Crystalline Endo, 154.7, 3.43% to ca 5.16 3.68 No change anhydrous source Salt formation melt 120° C. - loss of Suspension water Naphthalene-2- 95.88 1:1 Crystalline Endo, 232.5, Weight reduction 0.09 4.74 No change sulfonic Salt formation melt post endo Suspension 1-Hydroxy-2- 97.80 1:≈1.1 Poorly Two endos, NR 0.01 3.71 No change naphthoic crystalline 166.5 and Suspension No salt 180.6 - mixture formation of species Pyromellitic 97.49 1:≈1.25 Poorly Two endos, NR 0.17 2.27 Slight change crystalline 162.7 and Suspension Salt formation 199.2 - mixture of species ND—not determined, NR—not recorded

Example 2—Solubility of RPL554 Salts in Saline Solutions, Water and Aqueous Buffer Solutions at 25° C.

The behaviour of salts of RPL554 were examined under the following conditions:

-   -   Phosphate buffered to pH 3.5 in saline, 0.9% w/w at 25° C.     -   Acetate buffered to pH 4.5 in saline, 0.9% w/w at 25° C.     -   Citro-Phosphate buffered to pH 4.5 in saline, 0.9% w/w at 25° C.     -   Phosphate buffered to pH 6.5 in saline, 0.9% w/w at 25° C.     -   Saline, 0.7, 0.9 and 1.1% w/w at 25° C.     -   Deionised water at 25° C.

RPL554 salts and RPL554, ca 50 mg, were suspended in the various aqueous media, 1 ml, with agitation at the specified temperatures for 24 hours. The solids were isolated and dried in vacuo at 45° C. The retained filtrates were examined by HPLC.

Additional RPL554 methane sulfonate salt, ca 50 mg, was charged to the water mixtures at 25° C. and 37.5° C. in order to afford a suspension. In all other cases, suspensions were obtained.

The solubility of the RPL554 was determined by HPLC using a single point calibration and is expressed as RPL554 and not as the salt and are detailed in Table 6 and Table 7 for the various conditions utilised.

TABLE 6 Solubility as RPL554 (mg/ml) in saline and water at 25° C. 0.7 w/w % 0.9 w/w % 1.1 w/w % Counter ion Saline Saline Saline Water Phosphate 7.22 4.78 2.86 41.84 Methane sulfonate 5.01 3.73 2.52 44.52 Ethane-1,2-disulfonate 4.79 4.12 1.03 3.69 Hydrochloride 2.85 1.93 2.48 12.66 Sulfate 2.78 1.94 1.35 12.11 Benzenesulfonate 2.27 2.74 2.94 2.57 Ethanesulfonate 1.62 0.79 1.27 21.37 Hydrobromide 0.95 0.82 0.66 3.43 p-Toluenesulfonate 0.83 0.62 0.8 1.01 Naphthalene-2-sulfonate 0.17 0.09 0.09 0.13 Naphthalene-1,5- 0.01 0 0.01 0.01 disulfonate None (RPL554) 0 0 0 0

TABLE 7 Solubility as RPL554 (mg/ml) in buffer solution at 25° C. pH 3.5, pH 4.5, pH 4.5, Citro- pH 6.5, Counter ion Phosphate Acetate phosphate, Phosphate Ethane-1,2-disulfonate 2.66 1.47 4.14 — Phosphate 1.84 1.67 3.29 0.02 Methanesulfonate 1.72 2.01 3.10 0.02 Hydrochloride 1.07 1.38 1.93 0.02 Sulfate 1.22 0.42 1.75 0.00 Benzenesulfonate 1.10 1.39 1.57 0.00 Ethanesulfonate 1.18 0.46 1.55 0.00 Hydrobromide 0.33 0.71 0.75 0.00 p-Toluenesulfonate 0.18 0.77 0.61 0.00 Naphthalene-2- 0.08 0.41 0.28 0.00 sulfonate None (RPL554) 0.30 0.24 0.22 0.00 Naphthalene-1,5- 0.00 0.01 0.00 0.00 disulfonate

It has been shown that ethane-1,2-disulfonate, phosphate, methanesulfonate, hydrochloride, sulfate, benzenesulfonate and ethanesulfonate salts of RPL554 have particularly favourable solubility characteristics. In particular, the solubility in a pH 4.5 citro-phosphate buffer allows the production of higher concentration formulations with reduced acidity as compared with other salt solutions.

Example 3—Thermal Manipulation and Behaviour to Humidity

The nature of the hydration and a preliminary examination of salt robustness/polymorphism was assessed by thermal manipulation using ThermoGravimetric Analysis (TGA) and Gravimetric Vapor Sorption (GVS).

RPL554 hydrochloride showed reversible water uptake under ambient conditions with no change in form and is likely to be a stable version of the salt. No form change was detected by thermal manipulation of the salt below the melt endotherm.

The behaviour of the hydrochloride salt to humidity was studied by GVS over desorption, sorption and desorption cycles as illustrated in FIG. 4. The hydrochloride salt displayed reversible adsorption and desorption over the humidity range with no hysteresis. The salt was an anhydrate at 0% humidity and reversibly adsorbs water (up to 2 mole equivalents), up to 90% humidity. The XRPD patterns of RPL554 hydrochloride for 0% humidity (A), 90% humidity (B) and input form (C) are shown in FIG. 5, and demonstrated form stability over the humidity range, and reversible wetting/hydration.

The behaviour of the bis-RPL554 ethane-1,2-disulfonate to humidity by GVS over desorption, sorption and desorption cycles as illustrated in FIG. 6. The ethane-1,2-disulfonate salt displayed reversible adsorption and desorption over the humidity range with no hysteresis. The salt was an anhydrate at 0% humidity and adsorbs water (up to 5 mole equivalents), up to 90% humidity. The water uptake to 50% humidity equated to 4 mole equivalents, which then converted to 5 mole equivalents at 90% humidity.

The XRPD patterns, FIG. 7, of the bis-RPL554 ethane-1,2-disulfonate salt at 0 and 90% humidity were the same as the input form of the salt and demonstrated form stability over the humidity range and reversible wetting/hydration.

A summary of the results of the thermal and humidity tests is given in Table 7.

TABLE 7 Isothermal Counter ion 105° C., 2 hours Thermal cycle Behaviour to humidity Comment Hydrosulfate No form Form change by Tetrahydrate above 30% Disparity between change or XRPD humidity and an anhydrate isothermal and thermal significant Endotherms at at 0% humidity. Hysteresis cycle data - different weight 122 and 185° C. between 0 and 30% form behaviour. reduction. are removed. humidity and reversible. Thermal and humidity New endotherm Form change for anhydrate induced form changes at 219° C. and tetrahydrate. dependent upon the conditions with no cross correlation. Tetrahydrate form stable above 30% humidity. Phosphate Form change - Form change - Reversible adsorption and New thermal similar to similar to desorption over the characteristic exotherm RPL554 by RPL554 by humidity range with no and endotherm XRPD but not XRPD but not hysteresis. No salt coincident with weight DSC - DSC - (possible hydration, except for loss by TGA. (possible degradation) wetting. Form stability at Satisfactory behaviour degradation) extremes of humidity. to variable humidity with no form change. Hydrochloride Reversible Stable form Anhydrate at 0% humidity Reversible water water uptake. and dihydrate, up to 90% uptake, no form No form humidity with reversibility. change under thermal change. No hysteresis. Form or humidity stability at extremes of conditions. Reversible humidity. hydration of the salt. Ethane No variable No form change Monohydrate above 40% Disparity between sulfonate water uptake. by XRPD. humidity and an anhydrate isothermal and thermal No form Endotherm at at 0% humidity. Hysteresis cycle data - different change. 86° C. removed. between 0 and 40% form behaviour. No change in humidity and reversible. Monohydrate form main Form change for anhydrate stable above 40% endotherm, and mono-hydrate. humidity. Methane No variable Not conducted Reversible adsorption and No variable water sulfonate water uptake. desorption over the uptake or form change No form humidity range. Hysteresis under thermal change. between 30 and 70% conditions. Hysteresis humidity. Adsorption - di- between 30 and 70% hydrate at 70% humidity humidity and variable and tetra-hydrate at 90% hydration. humidity. Desorption - di- hydrate at 70% humidity and mono-hydrate at 40% humidity, converting to anhydrate at 0% humidity. Form change for an-hydrate and tetra-hydrate Ethane-1,2- No form Not conducted Reversible adsorption and No evidence of form disulfonate change. desorption over the change. Reversible humidity range with no adsorption and hysteresis. Anhydrate at 0% desorption over the humidity to tetrahydrate at humidity range with no 50% humidity and up to, hysteresis. ‘Loose’ non- pentahydrate at 90% formal hydration of the humidity. Form stability salt. and reversible hydration at extremes of humidity Benzene No form Not conducted Not conducted No evidence of form sulfonate change. change. Conclusion

On the basis of the above investigations into the solubility and stability of various salts of RPL554 it has been found that ethane-1,2-disulfonate, phosphate, methanesulfonate, hydrochloride, sulfate, benzenesulfonate, ethanesulfonate, hydrobromide and p-toluenesulfonate are the preferred salts of RPL554. The ethane-1,2-disulfonate, phosphate, methanesulfonate, hydrochloride, sulfate, benzenesulfonate and ethanesulfonate salts are particularly preferred. The ethane-1,2-disulfonate and hydrochloride salts have been found to have the most preferred properties on the basis of solubility and thermal stability at different humidities.

Further Development

Example 4—Formation and Characterisation of RPL554 Salts

RPL554 Salt Formations

Salt formations were carried out in three sets of three with the acids chosen, the solvent they were dissolved in to 2M concentration and the equivalents added to 7 g of the base in DCM shown in Table 8 (which sets out the acids used during the salt formation with volume and mmol calculations based in the relevant equivalents of 2M acid being added to 7 g RPL554 in DCM).

TABLE 8 Solvent for Acid Acid counter ion counter ion Equivalents Volume (ml) mmol Hydrochloric EtOH, 2M 4 29.32 58.63 Phosphoric EtOH, 2M 1 7.33 14.66 Methanesulfonic EtOH, 2M 4 29.32 58.63 Ethanesulfonic THF, 2M 1 7.33 14.66 Ethane-1,2-disulfonic EtOH, 2M 1 7.33 14.66 Sulfuric EtOH, 2M 1 7.33 14.66 Benzenesulfonic EtOH, 2M 4 29.32 58.63 p-Toluenesulfonic EtOH, 2M 4 29.32 58.63 Hydrobromic EtOH, 2M 4 29.32 58.63 Series 1

6.995, 7.005 and 7.004 g RPL554 were weighed into the first three flasks, charged with 410 ml DCM (based on the solubility of the base in DCM being 17 mg/ml), heated to 40° C. and stirred for 1 hour before the planned addition of ethanesulfonic, ethane-1,2-disulfonic and sulfuric acid respectively. However, the base did not dissolve in the given volume of DCM. An additional 50 ml was added to each flask and stirred at temperature for 30 minutes, but dissolution did not occur until a further 50 ml of DCM was added and stirred, delivering a clear, yellow solution. The three acids were charged to the appropriate flasks, with a lightening in the colour of the clear solution observed with the ethanesulfonic and sulfuric acid whereas ethane-1,2-disulfonic acid created a white precipitate upon addition. The three solutions were left to stir to at ambient temperature overnight.

The clear, pale yellow solution of the ethanesulfonate was reduced to ca. 20 ml, producing a clear, yellow solution which crystallised to give a mobile solid. TBME (tert-butyl methyl ether, 30 ml) was added and the suspension was stirred for ca. 1½ hours before isolating with a 25 ml TBME cake rinse, leaving a pale yellow solid.

The white, thin slurry suspension of the ethane-1,2-disulfonate was reduced to ca. 100 ml to thicken the slurry before isolating with a 25 ml TBME cake rinse, leaving an off-white solid.

The clear, pale yellow solution of the sulphate was reduced to ca. 20 ml, producing a clear, dark yellow solution. The addition of TBME (50 ml) initially caused a gum to form but trituration and stirring for ca. 3 hours yielded crystallised solids which were isolated with 30 ml TBME cake rinse, leaving a pale yellow solid.

The three salts were dried in vacuo at 60° C. for ca. 40 hours.

Series 2

Following the initial attempts to dissolve the RPL554 in 6.5 vol DCM, 6.993, 7.001 and 7.003 g RPL554 were weighed into the second set of three flasks before being charged with 500 ml DCM and stirred to 40° C. for ca. 45 minutes to achieve dissolution before the addition of benzenesulfonic, p-toluenesulfonic and hydrobromic acid respectively, causing the three yellow solutions to pale in colour, before allowing to stir to ambient.

The clear, pale yellow solution of the benzenesulfonate was left to stir overnight before reducing to ca. 30 ml then gradually adding 125 ml TBME which resulted in a precipitate that was stirred for ca. 30 minutes before isolating with a 25 ml TBME cake rinse, leaving a pale yellow solid.

Both the p-toluenesulfonate and hydrobromide solutions were reduced to 30 ml before the addition of 125 ml TBME to each then leaving to stir overnight. The p-toluenesulfonate had developed a mildly gummy solid that was able to be crushed down then stirred for ca. 2½ hours before isolation with a 25 ml TBME rinse, leaving a pale yellow solid, whereas the hydrobromide had yielded a sticky gum that required trituration to develop a seedbed before stirring for ca. 4 hours then isolating with a 25 ml TBME rinse, delivering an off-white solid.

The three salts were dried in vacuo at 60° C. for ca. 16 hours then at 45° C. for ca. 60 hours.

Series 3

7.005, 6.993 and 6.997 g RPL554 were weighed into the final set of three flasks before charging with 500 ml DCM and stirring to dissolution at 40° C. after ca. 30 minutes before the addition of hydrochloric, phosphoric and methanesulfonic acid respectively, causing the three yellow solutions to pale in colour, and leaving to stir ambient overnight for ca. 16 hours. The solutions were reduced to ca. 30 ml before the gradual addition of 125 ml TBME.

Both the hydrochloride and mesylate solutions formed strong, mobile precipitates that were left to stir for one hour before isolating with a 25 ml TBME cake rinse, delivering off-white solids.

The phosphate solution initially produced a gum upon the addition of TBME however physically crushing the lumps and allowing to stir for ca. 2 hours yielded a uniform slurry. Isolating with a 25 ml TBME cake rinse delivered yellow solids along with a bright yellow filtrate. These solids, along with the hydrochloride and mesylate, were dried in vacuo at 45° C. for ca. 60 hours.

As the other filtrates so far obtained were either colourless or very pale, the phosphate filtrate was reduced, delivering yellow solids which were isolated by filtration and dried in vacuo at 60° C. for ca. 16 hours.

The results of the salt formation, regarding recovery and fate, are summarised in Table 9. The ethanesulfonate and two phosphate salts were not carried forward into water maturation, based on previous investigations, and so underwent full analysis. Initial analysis of the hydrochloride by XRPD suggested that water maturation would be unnecessary, however analysis by DSC revealed slightly different thermal properties to the previously obtained salt and so the hydrochloride underwent water maturation.

TABLE 9 Salt Counter Ion Mass (g) Recovery (%)* H₂O Matured Hydrochloride 6.339 84.07 Yes Phosphate 4.812 87.56 No Phosphate 2.567 No Mesylate 12.774 Quantitative Yes Ethanesulfonate 8.588 99.77 No Ethane-1,2-disulfonate 8.207 97.70 Yes Sulphate 9.634 Quantitative Yes Benzenesulfonate 11.327 Quantitative Yes p-Toluenesulfonate 12.246 Quantitative Yes Hydrobromide 9.008 Quantitative Yes *The recovery is not indicative of active content, nor adjusted for solvents. Water Maturation of the RPL554 Salts

All of the salts besides the hydrochloride, phosphate and ethanesulfonate were slurried in water (30-60 ml) for ca. 21-22 hours at 20° C. and the hydrochloride was slurried in water (30 ml) for 6 hours at 22° C. Variation in the volumes of water used is due to the volume of water required to deliver sufficiently mobile suspensions. Benzenesulfonate, p-toluenesulfonate and the hydrobromide initially formed gums but prolonged stirring delivered mobile suspensions (clear form/version change).

All water matured salts were isolated with a damp cake water rinse before drying in vacuo at 60° C. for ca. 19 hours. Details of the mass input, recovery and water volumes are given in

TABLE 10 Table 10 Mass (g) Recovery Water Salt Counter Ion Input Out (%) added (ml) Hydrochloride 5.89 5.01 85.06 30 Mesylate 11.77 5.19 44.10 50 Ethane-1,2-disulfonate 7.15 6.37 89.10 50 Sulphate 8.66 6.69 77.25 50 Benzenesulfonate 10.25 7.54 73.56 30 p-Toluenesulfonate 11.24 8.24 73.31 60 Hydrobromide 8.01 6.24 77.90 60

The water matured salts generally all delivered either more crystalline material by XRPD than the input salt or delivered a salt that matches existing patterns, apart from the HCl salt which remained unchanged (as anticipated by XRPD, intended to improve thermals).

Because of this, a small sample (52.1 mg) of the hydrochloride salt was subject to a second extended water slurry (0.2 ml) for ca. 21 hours at 22° C. before isolation with a damp cake water rinse. The sample was dried in vacuo at 60° C. for ca. 18 hours, yielding 37.2 mg (71.40% recovery) of salt. Analysis by XRPD, DSC and TGA however revealed little difference to the input material and so extended water maturation of the rest of the RPL554.HCl salt was deemed unnecessary.

Example 5—Milling of RPL554 Salts

Tests were carried out to identify whether the RPL554 salt forms according to the invention can be milled satisfactorily. Scanning Electron Microscopy (SEM) and visible light microscopy were performed on the APIs pre- and post-micronisation.

The jet milling activity was performed using a single pass milling operation, at an experimentally dictated grinding pressure. Only material recovered from the micronised product outlet was retained; i.e. material that has coated the inside of the jet mill was not recovered. Qualitative assessment of the ease of micronisation was noted.

Jet-Milling Performance

Eight of the salts produced in Example 4 were milled. These salts were the ethanesulfonate salt, the p-toluenesulfonate salt, the mesylate (methanesulfonate) salt, the benzenesulfonate salt, the sulfate salt, the hydrochloride salt, the ethane-1,2-disulfonate hemi-salt and the hydrobromide salt.

All eight batches of sample salts were successfully jet milled with a Sturtevant jet-mill. All eight batches were processed with the following parameters: a grinding pressure of 60 PSI and a venture pressure of 80 PSI.

Before jet-milling, a pestle and mortar were used to lightly grind all sample powders, with the exception of the ethanesulfonate salt. This process step was incorporated to break down large aggregates that existed in a number of the sample batches. However, for the ethanesulfonate salt, the grinding was not necessary because the large aggregates could be easily broken down with the spatula.

Some differences in the milling behaviour of the sample powders was observed. In general, seven salts behaved similarly when jet-milled, with yields ranging from approximately 45% to 70% as shown in Table 11. It was observed that the ethanesulfonate, hydrochloride and hydrobromide salt were most readily milled compared to the other salts. In addition, all eight salts demonstrated a degree of cohesive behaviour before and after milling.

All the sample batches were subjected to SEM analysis pre- and post-jet-milling. The SEM analysis illustrated comparable qualitative particle sizes post jet milling for all materials. It is estimated that the particle size ranges approximately between 1 and 3 μm.

TABLE 11 Milling Input Output Yield Time Ease of Sample Salts (g) (g) (%) (min) Milling ethanesulfonate salt 3.89 2.75 70.7 5.0 Easy p-toluenesulfonate salt 7.80 4.26 54.6 12.0 Intermediate mesylate salt 4.94 2.22 44.9 9.5 Intermediate benzenesulfonate salt 7.22 4.20 58.2 7.0 Intermediate sulfate salt 6.21 1.31 21.1 15.0 Hard hydrochloride salt 4.56 2.60 57.0 6.0 Easy ethane-1,2-disulfonate 6.12 2.74 44.8 13.2 Intermediate hemi-salt hydrobromide salt 5.82 3.01 51.8 5.3 Easy

Example 6—Characterisation of Micronised Salts

The micronised salts were characterised by XRPD, DSC and TGA analysis. The majority of the salts were essentially unchanged by micronisation, other than the expected particle size reduction, which led to fine particles in all salts as observed by microscopy.

¹H NMR analysis of the micronised salts reveals no composition variance and generally reduced levels of residual solvent compared to the non-micronised salts.

Some differences in DSC profiles were observed with some salts. The methanesulfonate (mesylate), ethanesulfonate (esylate) and sulfate salts all showed broad endotherms around 100° C. that were not fully correlated to percentage weight loss in the TGA and may suggest some kind of thermal modification.

The TGA profiles generally exhibited endotherm-corresponding mass losses, although there was some variation in the amount of initial mass loss from 30° C. in all salts except for the hydrochloride and mesylate.

Example 7—Measurement of Intrinsic Dissolution Rate

The intrinsic dissolution rates of eight salts of RPL554 were measured to determine which salts had the most favourable dissolution properties.

Dissolution Study

The dissolution assay (pH-dependent sample dissolution) was investigated using the Sirius inForm.

Dissolution of a compressed tablet of the compound was monitored in a pH 7.0 aqueous dissolution experiment (0.15 M NaCl) at 37° C. using UV-absorption spectroscopy in 2 hour experiments. A tablet with a diameter of 3 mm, requiring approximate weights of 10 mg was compressed under a weight of 100 kg load force. Only one face of the tablet was exposed to the dissolution medium, which contained a 0.01 M acetate/phosphate buffer system to minimise perturbation of the experimental pH from dissolution of the drug.

Once the pH was adjusted to 7.0, the tablet disk was automatically lowered into the 40 mL aqueous media, allowing instantaneous data collection as soon as the sample was introduced. Stirring of the solution was continuous and at a constant rate of 100 rpm. The absorption data was converted to absolute sample weights using previously determined, pH-dependent, molar extinction coefficients. An appropriate wavelength range was chosen to ensure that spectroscopic data with an absorption value of <1.3 was analysed, avoiding erroneous dissolution results due to saturation of the UV light source.

The results of the dissolution experiments are shown in FIGS. 8 and 9. Every compound was measured in duplicate. Note that FIG. 8 shows the compound released in milligrams and FIG. 9 shows the compound released in micrograms.

The intrinsic dissolution rates of the salts are shown in Table 12.

TABLE 12 Mass of salt (μg) dissolved after 2 hours Salt Test 1 Test 2 Average sulfate salt 5910 6500 6205 ethanesulfonate salt 300 410 355 methanesulfonate salt 160 290 225 p-toluenesulfonate salt 51.2 71.9 61.6 benzenesulfonate salt 50.0 70.1 60.1 hydrochloride salt 31.7 39.4 35.6 hydrobromide salt 30.4 40.1 35.3 ethane-1,2-disulfonate salt 21.1 34.9 28.0 free base 10.0 17.0 13.5

The dissolution plots shows that all salts dissolved in a greater amount than the free base after 2 hour experiments at the same conditions. Three salts; sulfate, methanesulfonate and ethanesulfonate, showed higher dissolution than the rest of the salts as is shown in FIG. 8. It should be noted that the maximum pH change (from a nominal start pH of pH7) was about 0.15 pH units decrease, which was for the sulfate salt. The methanesulfonate was about 0.1 pH units decrease. The rest of the salts decreased by less than 0.06 pH units.

In FIG. 9 the free base was plotted with the five other salts (ethane-1,2-disulfonate, HBr, HCl, benzenesulfonate and p-toluenesulfonate) and showed less amount of sample released for the same experiments.

Particular behaviour observed for the methanesulfonate salt showed a high release in the first 20 minutes, with 3960 μg dissolved at 8.5 min and 5200 μg dissolved at 11 min, followed by precipitation (FIG. 8). The ethanesulfonate showed a less pronounced initial peak in dissolution (600 μg at 5.7 min and 700 μg at 13 min).

The sulfate salt showed a high release initially and it was expected that this sample would also precipitate if given enough time; hence another experiment was performed increasing the time of the experiment to 24 hours (FIG. 10). The behaviour observed in FIG. 10 was similar to the previous sulfate salt experiments for the first two hours. Thereafter, the sample did start to precipitate slowly but still remained highly supersaturated even after 24 hrs.

The salts of RPL554 were shown to all have improved intrinsic dissolution rates compared with free base, with some salts (sulfate, methanesulfonate and ethanesulfonate) showing particularly high dissolution rates.

Enhanced dissolution rates of the salts could potentially greatly increase both the speed and extent of drug availability in the lung from pMDI, DPI and nevulised suspension formulations. This could facilitate the modulation of pharmacokinetics of the drug to change both the onset and duration of activity. The more rapid dissolution without changing the pH of the buffer system indicates this dissolution could occur without potential irritation of the lung which might be induced by lower pH formulations.

Example 8—Evaluation of RPL554 and Salt Variations in pMDI and DPI Formulations

Methods

HPLC Assay Analysis

A validated high performance liquid chromatography (HPLC) method (Intertek Melbourn scientific analytical method AM/358/01) for the determination of the aerodynamic droplet size distribution of RPL554 suspensions for nebulisation was used.

The assay was performed using an Agilent (Agilent Technologies Ltd, UK) 1200 series HPLC system consisting of: isocratic pump, variable wavelength detector, autosampler, thermostatted column compartment and utilised Chemstation LC software, Rev. B04.02.

The following chromatography conditions were used: Column: Waters X Bridge phenyl, 3.5 μm, 150×4.6 mm, (Part number 186003335); Diluent: Acetonitrile:Water (50:50, v/v); Mobile Phase: Acetonitrile: Water: Trifluoroacetic acid (45:55:1 (v/v)); Flow Rate: 1.5 mL/min; Injection Volume: 10 μL; Detection: UV @ 254 nm; Column Temperature: 40° C.; Autosampler Tray Temperature: Ambient; Run Time: 6 minutes.

HPLC Stability Analysis

A validated HPLC method (Onyx-Scientific, Final product testing monograph for RPL554) for the determination of chemical purity by HPLC was used.

The assay was performed using an Agilent (Agilent Technologies Ltd, UK) 1200 series HPLC system consisting of: Quaternary Pump, Multiple Wavelength Detector, Autosampler, Thermostatted Column Compartment, Degasser and utilised Chemstation LC Software Rev. B.04.02

The following chromatography conditions were used: Column: Waters X Bridge phenyl, 3.5 μm, 150×4.6 mm, (Part number 186003335); Diluent: Acetonitrile:Water (50:50, v/v); Mobile Phase: A—Purified Water:Trifluoroacetic acid (100:0.1); B—Acetonitrile:Trifluoroacetic acid (100:0.1); Flow Rate: 1.0 mL/min; Injection Volume: 10 μl; Detection: UV @ 254 nm; Column Temperature: 30° C.; Post Run: 5 min; Gradient: [Time (min): % A:% B]: [0:95:5], [2:95:5]; [15:5:95], [20:5:95], [22:95:5].

Primary Particle Size Analysis

A Mastersizer 2000 fitted with a Scirocco 2000 dry powder dispersion unit (Malvern Instruments Ltd, UK) was used to analyse the primary particle size of the micronised RPL554 and salt variants. The salts (50 mg) were automatically sampled via a vibrating feed control at a feeder rate of 60% and dispersed in compressed air at a pressure of 3 bar.

Visual inspection of the compounds indicated that the powders demonstrated a degree of cohesive behaviour, with small aggregates existing within the mass of powder. However, there was no need to further de-aggregate these before analyses.

pMDI Manufacture

pMDI formulations containing a 6 mL fill of either HFA 134a, HFA 227 or 50:50 w/w blend of HFA 134a: 227 were prepared in 19 mL PET bottles. Each PET bottle contained 24 mg of RPL554 or salt variation, and was sealed with a 50 μL KHFA valve to provide 200 μg salt/actuation. Due to differences in the molecular weights of the RPL554 salt forms, the amount of RPL554 base equivalent emitted per actuation varied as a function of the molecular weight of each salt. The formulations were prepared with no adjustment for differences in molecular weight of the salts.

For each propellant and for the propellant blend, pMDI's were also formulated to contain 10% (w/w) absolute ethanol containing 0.1% (w/w) Tween® 80 (referred to as ethanol/Tween). The formulation constituents are shown in the tables below.

HFA 134a Per Canister mL g % w/w % w/w (ex-drug) HFA 134a 6.0000 7.3080 99.6727 100.0000 HFA 277ea Ethanol 0.0000 Tween 80 0.0000 RPL554 Salt 0.0240 0.3273 Totals 6.0000 7.3320 100.0000

HFA 134a 10% Ethanol Per Canister mL g % w/w % w/w (ex - drug) HFA 134a 5.3940 6.5699 89.6057 89.900 HFA 227ea Ethanol 0.9276 0.7308 9.9673 10.000 Tween 80 0.0069 0.0073 0.0997 0.100 RPL554 Salt 0.0240 0.3273 Totals 6.3216 7.3320 100.0000

HFA134a:HFA 227a Per Canister mL g % w/w % w/w (ex - drug) HFA 134a 3.0000 3.6540 46.3823 46.5241 HFA 227ea 3.0000 4.2000 53.3130 53.4759 Ethanol 0.0000 Tween 80 0.0000 RPL554 Salt 0.0240 0.3046 Totals 6.0000 7.8780 100.0000

HFA134a:HFA 227a 10% Ethanol Per Canister mL g % w/w % w/w (ex - drug) HFA 134a 2.6970 3.2849 41.6977 41.8251 HFA 227ea 2.6970 3.7758 47.9284 48.0749 Ethanol 0.9970 0.7854 9.9695 10.0000 Tween 80 0.0074 0.007854 0.0997 0.1000 RPL554 Salt 0.0240 0.3046 Totals 6.3910 7.8780 100.0000

HFA 227a Per Canister mL g % w/w % w/w (ex - drug) HFA 134a HFA 227ea 6.0000 8.4000 99.7151 100.0000 Ethanol 0.0000 Tween 80 0.0000 RPL554 Salt 0.0240 0.2849 Totals 6.0000 8.4240 100.0000

HFA 227a 10% Ethanol Per Canister mL g % w/w % w/w (ex - drug) HFA 134a HFA 227ea 5.3940 7.5516 89.6439 89.9000 Ethanol 1.0663 0.8400 9.9715 10.0000 Tween 80 0.0079 0.0084 0.0997 0.1000 RPL554 Salt 0.0240 0.2849 Totals 6.4603 8.4240 100.0000

The stock solution of Tween 80 in absolute ethanol was prepared at a concentration of 1% w/w. Thus the addition of small amounts of Tween® 80 required for the formulations was achieved by the use of the ethanol/Tween solutions as shown in the above tables.

In total 54 pMDI samples were prepared.

Visual Assessment of pMDI Formulations

Preliminary assessments of the physical properties of the pMDI formulations were based on visual indicators i.e. solubility, flocculation, sedimentation and creaming.

The information relating to assessment of physical properties was recorded in the form of digital photographic images. Digital pictures of the pMDI bottles were recorded immediately after shaking the formulations, and thereafter at intervals over a period of up to 3 minutes, images were also taken after the contents of the PET bottles had been left undisturbed in excess of five minutes. Furthermore the ease and extent of dispersion, flocculation, and the sedimentation (or creaming) rate and sedimentation (or creaming) height were also scored.

Based on the results of the physical assessment, six formulations were selected for aerosol characterisation tests.

Solubility Measurements of RPL554 and Salts in Selected pMDI Formulations

Quantitative assessment of the solubility of RPL554 and salt variants in the propellant systems of selected pMDI formulations (three replicates of each formulation) was performed.

pMDIs were directly coupled to an adaptor fitted with a 0.20 μm filter unit connected, in series to a 21 G needle, which was inserted via a rubber septum, into a cooled multi-dose glass vial. A 19 G filter needle was inserted through the septum to aid evaporation of propellant from the vial. Prior to the filtration process the vial was cooled in a mixture of dry ice and acetone to ensure that the pressure within the vial was reduced in order to facilitate collection of the output from the pMDI. Ten consecutive actuations of the pMDI were fired through the filter and collected in the vial. Between actuations the canister was shaken for approximately 10 seconds. The pMDI unit was weighed before and after the filtering procedure. The filtrate was stored at room temperature and allowed to evaporate to dryness.

Samples were recovered by carefully rinsing the inside of the vials with 1 mL of recovery solution before transfer to HPLC vials for analysis. The estimated % of RPL554 solubilised within the canister was calculated from the starting mass of RPL554 within the canisters, which in turn was calculated using the theoretical molecular weight values of the RPL554 free base and salt variants shown in Table 13. The theoretical molecular weight estimates of the salts were provided by Verona. (All were considered as 1:1 stoichiometric salts, except for the ethane-1,2-disulfonate which was confirmed to be a hemi-salt.)

TABLE 13 Calculated Calculated mass metered dose Theoretical of RPL554 (μg) RPL554 Molecular base within base per RPL554 Variant Weights canister (mg) actuation Free Base 477.56 *24.0 200 Ethanesulfonate 587.69 19.5 163 p-Toluenesulfonate 649.78 17.6 147 Methanesulfonate 573.67 20.0 166 Benzenesulfonate 635.74 18.0 150 Sulfate 575.64 19.9 166 Hydrochloride 514.02 22.3 186 Ethane-1,2- 572.65 20.0 167 disulfonate Hydrobromide 558.47 20.5 171 Aerosol Characterisation Tests of pMDI Formulations

Inertial impaction tests were performed using the Next Generation Impactor (NGI) under standard conditions i.e. 30 L/min flow rate, with the addition of a final external filter, to capture RPL554 variant that may have been solubilised. The emitted dose (ED, μg), fine particle dose (FPD, μg) and fine particle fraction (FPF, %) were evaluated. The assessments were performed at the beginning of canister life, and 5 consecutive actuations were fired into the NGI using a 0.25 mm orifice diameter actuator (NMX). Between actuations the canister was removed from the NGI inlet and shaken for approximately 15 seconds. RPL554 was quantitatively recovered from the actuator, induction port, each of the NGI collection stages and the external filter with 10 mL of diluent. The volume of diluent (50% acetonitrile in HPLC grade water) used for each sample was selected to ensure RPL554 concentrations were above the limits of quantitation of the HPLC assay method (0.06 μg/mL).

Dry Powder Inhaler RPL554 Free Base and Salt:Lactose Powder Blends

RPL554 and salt variations were prepared as DPI formulations using lactose as the excipient.

Batches (approximately 5 g) of 1% w/w RPL554 free base or salt variants: lactose blends were prepared. In brief, the RPL554 free base or salt plus a small quantity of lactose was passed through a 38 μm sieve. The sieved material plus the remaining lactose was mixed in a glass mortar prior to transfer to a stainless steel screw cap jar and further mixing (10 minutes at 46 rpm) conducted using a Turbula blender. The composition of the dry powder blend was 0.05 g API and 4.95 g lactose.

In order to determine the content uniformity of the blends, aliquots (approx. 20 mg) of powder were sampled from each blend, accurately weighed, and diluted to volume in 10 mL volumetric flasks with diluent. The flasks were sonicated for 3 minutes before samples were transferred to HPLC vials for analysis.

Aerosol Performance of DPI Formulations

Capsules were hand filled with 20 mg of the 1% w/w RPL554 free base or salt variants: lactose blends, i.e. 200 μg salt per capsule, the fill weight of each capsule was recorded. Due to differences in the molecular weights of the RPL554 salt forms, the amount of RPL554 emitted per actuation varied as a function of molecular weight. The formulations were prepared with no adjustment for differences in molecular weight of the salts.

The powders were delivered via the Cyclohaler DPI (PCH Pharmachemie, BV, The Netherlands). The Cyclohaler® DPI is a low resistance device and was operated at a flow rate of 90 L/min for 2.7 seconds. The cut off diameters for the NGI collection stages were calculated for the 90 L/min flow rate using the NGI User Guide (MSP Corporation, 2008).

The ED, FPD and FPF were determined from inertial impaction tests performed following the deposition of 5 capsules of each formulation into the NGI. For each capsule tested the combined weight of the Cyclohaler® and capsule was determined before and after operation to check that the dose had been delivered. The NGI was fitted with a pre-separator for these determinations. The central cup of the pre-separator was filled with 15 mL of diluent. Following deposition, the solution was recovered in a 20 mL volumetric flask and made up to volume with diluent. RPL554 was quantitatively recovered from the device, induction port and each of the NGI collection stages with 10 mL of diluent.

The volume of diluent used for each sample was selected to ensure RPL554 concentrations were above the limit of quantitation.

Stability Assessment of RPL554 and Salts: Lactose Powder Blends

Samples of 1% w/w RPL554 free base or salt variants: lactose blends were prepared and stored at elevated temperature (70° C.) for seven days, control samples were stored at ambient conditions and protected from light on the laboratory bench. All samples (approximately 0.5 g) were accurately weighed into screw cap glass scintillation vials (20 mL). For storage at elevated temperature samples were placed in an oven at 70° C. protected from light. Control sample vials were capped, protected from light and stored on the bench for 7 days.

In addition, to the RPL554 and salt variant blends, samples of lactose alone were also stored at the elevated temperature condition (control samples at ambient). The lactose only samples served as baseline data for the HPLC analysis. HPLC traces produced from the lactose only samples were subtracted from the traces in order to account for non-drug associated peaks.

Results and Discussions

Primary Particle Size Analysis

Table 14 shows the particle size distribution of the micronised RPL554 and salt variants as measured using laser light diffraction and shown as mean values, n=3 measurements. The results indicated that the salts were suitably micronised for formulation as a respiratory product, all D(0.9) values were less than 5 μm.

TABLE 14 RPL554 Variant D (0.1) (μm) D (0.5) (μm) D (0.9) (μm) Free base 0.58 1.37 3.00 Ethanesulfonate 0.56 1.43 4.18 p-Toluenesulfonate 0.47 1.34 4.53 Methanesulfonate 0.45 1.20 3.46 Benzenesulfonate 0.46 1.23 3.51 Sulfate 0.51 1.12 2.30 Hydrochloride 0.53 1.37 3.47 Ethane-1,2 disulfonate 0.52 1.25 2.78 Hydrobromide 0.64 1.52 3.23 Pressurised Metered Dose Inhaler Assessments Visual Assessment of pMDI Formulations

pMDI formulations of each RPL554 free base and salt variant for each of the different combinations of propellant (HFA 134a, HFA 227 or 50:50 (w/w) HFA 134a: 227), ethanol/Tween were scored in terms of dispersibility, flocculation, sedimentation (or creaming) rate and sedimentation (or creaming) height and based on these observations the potential of suitability for formulation as pMDI.

For the visually assessed variables, many of the formulations displayed very similar characteristics.

It was decided, that in addition to the RPL554 free base in 50:50 propellant containing ethanol/Tween the remaining chosen pMDI formulations to be assessed by inertial impaction analysis were as follows:

-   -   1. RPL554 free base HFA 134a/227 and ethanol/Tween     -   2. RPL554 ethanesulfonate HFA 227     -   3. RPL554 methanesulfonate HFA 134a     -   4. RPL554 benzenesulfonate HFA 134a     -   5. RPL554 sulfate HFA 134a     -   6. RPL554 ethane-1,2-disulfonate HFA 227 and ethanol/Tween         Solubility Measurements of RPL554 Free Base and Salts in         Selected pMDI Systems

The solubilities of the RPL554 free base and 8 salt variants in HFA 134a are shown in Table 15. From the visual assessments, none of the formulations demonstrated clear signs of solubility within the propellant. However, from the results of solubility testing, the ethanesulfonate and p-toluensulfonate salts demonstrated quantifiable levels of solubility.

The solubilities of the RPL554 free base and 8 salt variants in HFA 134a and ethanol/Tween are shown in Table 16. From the visual assessments, some of the formulations demonstrated signs of solubility within the propellant. The solubility testing of the formulations demonstrated that the addition of ethanol/Tween had an effect on the solubility of RPL554 within the propellant. All formulations demonstrated detectable levels of solubility, ranging from the lowest with ethane-1,2-disulfonate (5 μg/g) to the highest with methanesulfonate (298 μg/g).

The solubility of the RPL554 free base and 8 salt variants in HFA 227 was assessed, however, there were no quantifiable levels within the samples (Table 17).

Further solubility measurements were performed for two formulations that demonstrated interesting physical properties for selection as candidates for inertial impaction tests. Table 18 illustrates the quantifiable levels of RPL554 solubility for ethane-1,2 disulfonate in HFA 227 and ethanol/Tween and for the free base in HFA 134:227 and ethanol/Tween. In both cases, the fraction of solubilised RPL554 represented less than 1% of the drug present in the formulation.

TABLE 15 Solubility in HFA 134 Calculated Solubilised Calculated Solubility RPL554 μg RPL554 RPL554 per 50 μL solubilised RPL554 Variant (μg/g) actuation (%) Free Base BLQ BLQ BLQ Ethanesulfonate 126.81 9.03 5.56 p-Toluenesulfonate  1.56 0.11 0.08 Methanesulfonate BLQ BLQ BLQ Benzenesulfonate BLQ BLQ BLQ Sulfate BLQ BLQ BLQ Hydrochloride BLQ BLQ BLQ Ethane-1,2-disulfonate BLQ BLQ BLQ hemi-salt Hydrobromide BLQ BLQ BLQ *BLQ—below limit of quantitation (0.06 μg/mL)

TABLE 16 Solubility in HFA 134 with Ethanol/Tween Estimated Solubilised Estimated Solubility RPL554 μg RPL554 RPL554 per 50 μL solubilised RPL554 Variant (μg/g) actuation (%) Free Base 16.45 1.12 0.56 Ethanesulfonate 266.59 17.81 10.96 p-Toluenesulfonate 152.85 10.58 7.20 Methanesulfonate 298.07 19.38 11.64 Benzenesulfonate 90.57 6.05 4.03 Sulfate 73.19 4.71 2.84 Hydrochloride 149.17 9.79 5.27 Ethane-1,2-disulfonate 5.13 0.34 0.20 hemi-salt Hydrobromide 96.27 6.40 3.74

TABLE 17 Solubility in HFA 227 Calculated Solubilised Calculated Solubility RPL554 μg RPL554 RPL554 per 50 μL solubilised RPL554 Variant (μg/g) actuation (%) Free Base BLQ BLQ BLQ Ethanesulfonate BLQ BLQ BLQ p-Toluenesulfonate BLQ BLQ BLQ Methanesulfonate BLQ BLQ BLQ Benzenesulfonate BLQ BLQ BLQ Sulfate BLQ BLQ BLQ Hydrochloride BLQ BLQ BLQ Ethane-1,2-disulfonate BLQ BLQ BLQ hemi-salt Hydrobromide BLQ BLQ BLQ

TABLE 18 Estimated Solubilised Estimated Solubility RPL554 μg RPL554 RPL554 per 50 μL solubilised RPL554 Variant (μg/g) actuation (%) Ethane-1,2-disulfonate 1.69 0.11 0.07 hemi-salt - HFA 227:10% Ethanol:0.1% Tween Free base - HFA 134a:227:10% 16.11 1.06 0.53 Ethanol:0.1% Tween Inertial Impaction Testing of pMDI Formulations

FIG. 11 shows the recovery of the pMDI formulations following collection in the NGI. Deposition was promising with large amounts of material displaying aerodynamic properties suitable for inhalation, FPF values (i.e. % particles<5 μm ex-actuator) ranged from 48.2 to 81.0%, with methanesulfonate in HFA 134a displaying the highest FPF. The Induction Port (inlet throat) deposition was predominantly less than 20%, with the exception of the free base (50:50 propellant with ethanol/Tween) and ethane-1,2-disulfonate (HFA 227 with ethanol/Tween) formulations.

The mean metered doses in Table 19 (mean values, n=3, ±SD) shows the RPL554 recovery ranged from 53-75% of the theoretical metered dose (assuming no adsorption) shown in Table 13.

TABLE 19 Ethane- Methane- RPL554 Variant Free base sulfonate sulfonate Metered Weight (mg) 66.18 ± 0.2 77.56 ± 0.2 70.29 ± 0.7 Metered dose per 138.60 ± 1.6  105.28 ± 1.4  105.71 ± 2.9  Actuation (μg) % of Free Base on  6.97 ± 0.6 11.06 ± 1.5 10.29 ± 0.8 Actuator Emitted Dose per 128.93 ± 0.8  93.65 ± 2.7 94.84 ± 2.9 Actuation (μg) FPF (% <5 μm) 60.22 ± 1.6 79.66 ± 2.0 81.02 ± 1.6 MMAD (μm)  1.35 ± 0.1  2.20 ± 0.1  1.84 ± 0.1 GSD  2.62 ± 0.1  1.99 ± 0.1  2.11 ± 0.02 FPD (μg <5 μm) 77.63 ± 2.1 74.59 ± 2.5 76.81 ± 1.6 Benzene- Ethane-1,2- RPL554 Variant sulfonate Sulfate Disulfonate Metered Weight (mg) 72.69 ± 0.1 70.08 ± 0.2 66.71 ± 0.2 Metered dose per 112.48 ± 2.6  87.24 ± 1.4 107.41 ± 1.6  Actuation (μg) % of Free Base on  9.13 ± 0.4  8.03 ± 1.5  6.77 ± 0.2 Actuator Emitted Dose per 102.21 ± 2.3  80.25 ± 2.3 100.14 ± 1.2  Actuation (μg) FPF (% <5 μm) 76.41 ± 2.0 75.69 ± 3.4 48.15 ± 1.2 MMAD (μm)  2.20 ± 0.2  1.60 ± 0.1  1.84 ± 0.1 GSD  1.99 ± 0.04  2.44 ± 0.03  3.48 ± 0.3 FPD (μg <5 μm) 78.08 ± 2.3 60.74 ± 3.2 48.21 ± 0.8 RPL554 Free base in 50:50 propellant and ethanol/Tween; RPL554 Ethanesulfonate in HFA 227; RPL554 Methanesulfonate, Benzenesulfonate and Sulfate in HFA 134a and RPL554 Ethane-1,2-disulfonate in HFA 227 and ethanol/Tween. Dry Powder Inhaler Assessments

Single batches containing 1% w/w of RPL554 free base or salt: lactose were prepared.

Samples of each blend were tested to determine the RPL554 base content and the aerodynamic properties of each blend were also tested. Samples of the preparations were also stored at elevated temperature (70° C.) for seven days to assess stability.

Dry Powder Inhaler RPL554 Free Base and Salt: Lactose Powder Blends

The RPL554: lactose powder blends were prepared under temperature and humidity conditions of 17° C. and 56% RH. The measured RPL554 content of blends demonstrated close agreement with the theoretical content, as shown in Table 20, (calculated from molecular weights in Table 13) for the free base, ethanesulfonate and methanesulfonate (mean values, n=3, ±SD). The remaining blends, with the exception of the sulfate, gave values between 80 and 90% of the theoretical values. The lower figure for the sulfate salt reflects the lower purity of the input material (known to contain an impurity at a level of ˜15% area by HPLC-UV). However, all the blends were found to have content uniformity of less than 5% RSD and therefore deemed suitable for further testing, given that the purity and water content of the salts were not known at the date of testing.

TABLE 20 Total RPL554 Theoretical Recovered Recovered RPL554 Content RPL554 Content RPL554 Variant (μg) μg (1% w/w) (% Theoretical) Base 194.17 ± 3.2 201.33 ± 1.5 96.44 ± 0.9 Ethanesulfonate 161.89 ± 2.4 163.88 ± 0.5 98.79 ± 1.3 p-Toluene- 130.98 ± 1.9 147.73 ± 0.7 88.66 ± 1.1 sulfonate Methanesulfonate 165.05 ± 2.9 166.49 ± 0.0 99.13 ± 1.7 Benzenesulfonate 134.89 ± 1.2 150.99 ± 0.8 89.34 ± 0.5 Sulfate 122.77 ± 2.8 167.03 ± 1.0 73.50 ± 1.3 Hydrochloride 158.44 ± 4.4 187.67 ± 1.9 84.42 ± 1.9 Ethane-1,2- 135.96 ± 3.0 169.57 ± 0.5 80.18 ± 1.6 disulfonate Hydrobromide 143.99 ± 0.6 172.73 ± 2.3 83.37 ± 0.8 Aerosol Performance of DPI Formulations

The weight of the Cyclohaler® plus capsule was determined before and after each dose was delivered in order to estimate the total mass of powder blend delivered for each NGI determination. The total delivered doses estimated from weight measurements are shown in Table 21 (5 capsules containing 20 mg of powder blend (200 μg free base or salt/capsule)) via Cyclohaler®; all values expressed as RPL554 base except *). The table also shows the calculation of the masses of RPL554 base delivered for each RPL554 variant. This figure was adjusted to take into account the actual RPL554 base content (i.e. % theoretical) of each of the blends. The total μg of recovered RPL554 base, determined by HPLC analysis of samples from the NGI is also shown. Mass balance i.e. actual recovery (HPLC analysis)/calculated recovery (mass measurements) indicated that for all 9 formulations 64-74% recovery was achieved.

TABLE 21 * Theoretical Theoretical μg RPL554 μg RPL554 Measured **Adjusted Variant per per 20 mg, Blend RPL554 20 mg of 1% 1% w/w Blend Content (% Content per RPL554 Variant w/w Blend in each capsule Theoretical) capsule (μg) Free Base 200 200.00 96.44 192.87 Ethanesulfonate 200 162.52 98.79 160.55 p-Toluene- 200 146.99 88.66 130.33 sulfonate Methanesulfonate 200 166.49 99.13 165.05 Benzenesulfonate 200 150.24 89.34 134.22 Sulfate 200 165.92 73.50 121.95 Hydrochloride 200 185.81 84.42 156.86 Ethane-1,2- 200 166.79 80.18 133.73 disulfonate Hydrobromide 200 171.02 83.37 142.58 †Measured Calculated Mass of 1% RPL554 ††RPL554 w/w Blend Content Emitted % Delivered per (μg) per (μg) per Recovery RPL554 Variant capsule (mg) capsule (A) capsule (B) (B/A) Free Base 20.12 194.03 133.59 68.85 Ethanesulfonate 20.18 162.00 111.09 68.57 p-Toluene- 20.02 130.46 86.84 66.57 sulfonate Methanesulfonate 19.96 164.72 118.69 72.06 Benzenesulfonate 20.04 134.49 87.57 65.11 Sulfate 19.78 120.61 79.35 65.79 Hydrochloride 20.14 157.96 102.27 64.75 Ethane-1,2- 19.90 133.06 87.91 66.07 disulfonate Hydrobromide 19.96 142.29 104.28 73.29 **Adjusted for measured blend content (% theoretical - see Table 3.4.1.1) †Mass determined from weight change of capsule-loaded device ††Mass determined from HPLC analysis of recovered samples

The particle size distributions of free base and salts aerosolised using the Cyclohaler are shown in FIG. 12 and summaries of the key performance indicators are shown in Table 22 (formulated as 1% w/w lactose blends and delivered via the Cyclohaler® DPI; five capsules each containing 20 mg of powder blend (200 μg RPL554 variant/capsule) were used for each determination).

The minimum FPF was observed for the hydrobromide formulation (29.43%); for all other blends the FPF exceeded 30%, with a maximum value of 46.29% determined for the hydrochloride salt. The minimum fine particle dose (RPL554 base equivalent) was 23.28 for the sulfate salt formulation, while the maximum was 43.31 μg for the free base blend, reflecting the differences in the metered dose (and in the case of the sulfate salt, additionally the lower purity of the input material). MMAD values were within the range of 1.72 μm to 2.31 μm.

TABLE 22 RPL554 Variant FB ES PT MS BS Recovered RPL554 133.59 111.09 86.84 118.69 87.57 base/Capsule (ex-capsule) (μg) Emitted Dose 123.05 100.75 77.79 111.01 77.30 of RPL554 base/Capsule (ex-device) (μg) FPF (% <5 μm) 35.20 38.70 35.37 38.18 36.99 MMAD (μm) 1.99 1.87 1.74 2.00 1.91 GSD 2.63 2.57 2.55 2.40 2.57 FPD RPL554 base 43.31 38.99 27.52 42.39 28.59 (μg <5 μm) (ex-device) RPL554 Variant SF HC ED HB Recovered RPL554 79.35 102.27 87.91 104.28 base/Capsule (ex-capsule) (μg) Emitted Dose 70.71 92.97 79.95 93.20 of RPL554 base/Capsule (ex-device) (μg) FPF (% <5 μm) 32.93 46.29 40.39 29.43 MMAD (μm) 2.10 1.72 1.96 2.31 GSD 2.69 2.42 2.42 2.24 FPD RPL554 base 23.28 43.04 32.29 27.43 (μg <5 μm) (ex-device) Key: FB—Free Base; ES—Ethanesulfonate; PT—p-Toluenesulfonate; MS—Methanesulfonate; BS—Benzenesulfonate; SF—Sulfate; HC—Hydrochloride; ED—Ethane-1,2-disulfonate; HB—Hydrobromide.

Particularly favourable fine particle fractions (FPFs) were observed for the hydrochloride and ethane-1,2-disulfonate salts.

Stability Assessment of Blends of RPL554 Variants: Lactose Powder Blends

No visible changes to the appearance of the powders were observed. In all cases except the sulfate salt, the peak area of the RPL554 from the different salt forms accounted for 96-99% of the total areas, after storage at both room and elevated temperatures. The sulfate salt showed only 82% of the total area, but this reflects the purity of the input material and is not suggestive of degradation. There does not appear to be any degradation caused by storage either at room temperature or at 70° C. for the free base or any of the salts. 

The invention claimed is:
 1. A pharmaceutically acceptable acid addition salt of: (i) 9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one (RPL554); and (ii) ethane-1,2-disulfonic acid.
 2. A pharmaceutically acceptable acid addition salt according to claim 1, which is RPL554 ethane-1,2-disulfonate.
 3. A pharmaceutical composition comprising: (a) a pharmaceutically acceptable acid addition salt of (i) 9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one (RPL554) and (ii) ethane-1,2-disulfonic acid; and (b) a pharmaceutically acceptable excipient, carrier or diluent.
 4. A pharmaceutical composition according to claim 3, which is formulated for administration by inhalation.
 5. A pharmaceutical composition according to claim 3, which is a dry powder.
 6. A pharmaceutical composition according to claim 3, which is produced by dissolving a pharmaceutically acceptable acid addition salt of (i) 9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one (RPL554) and (ii) ethane-1,2-disulfonic acid.
 7. A pharmaceutical composition according to claim 6, wherein the aqueous solution is a buffered aqueous solution.
 8. A pharmaceutical composition according to claim 7, wherein the buffered aqueous solution comprises a phosphate buffer, a citrate buffer or a citro-phosphate buffer.
 9. A pharmaceutical composition according to claim 6, wherein the pH of the pharmaceutical composition is greater than or equal to about 2.5.
 10. A pharmaceutical composition according to claim 6, wherein the pharmaceutically acceptable acid addition salt is present at a concentration of greater than or equal to about 1.0 mg/ml.
 11. A method of treating or preventing a disease or condition selected from asthma, allergic asthma, hay fever, allergic rhinitis, bronchitis, emphysema, bronchiectasis, chronic obstructive pulmonary disease (COPD), adult respiratory distress syndrome (ARDS), steroid resistant asthma, severe asthma, paediatric asthma, cystic fibrosis, lung fibrosis, pulmonary fibrosis, interstitial lung disease, skin disorders, atopic dermatitis, psoriasis, ocular inflammation, cerebral ischaemia, inflammatory diseases and auto-immune diseases in a subject, which method comprises administering to said subject an effective amount of a pharmaceutically acceptable acid addition salt of (i) 9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one (RPL554) and (ii) ethane-1,2-disulfonic acid.
 12. A method of treating or preventing a disease or condition according to claim 11, wherein the disease or condition is chronic obstructive pulmonary disease (COPD). 